NASA finds crashing spacecraft into asteroids is a viable defence strategy

Dimorphos's trajectory was significantly altered by rebound from the DART collision.

According to study released on Wednesday, the asteroid Dimorphos' trajectory was changed more by dust and rock plumes that were thrown up from its surface after NASA's DART probe collided with it than by the kinetic impact alone.

During the Double Asteroid Redirection Test mission in October of last year, scientists effectively modified the location of an astronomical substance in space for the first time in history. To test whether it was feasible to deviate an asteroid system from its initial orbit, a 610kg (1,345lb) spacecraft was programmed to collide head-on with a pair of asteroids.

DART achieved great achievement. Its trajectory was reduced by 33 minutes as a result of the impact from the collision with Dimorphos; it now revolves around its parent asteroid, Didymos, in less than 11 and a half hours. The shift is much more pronounced than was anticipated.

Dimorphos's momentum was altered more by material released from its surface during the encounter than by the impact of DART, according to analysis of the experiment's data.

According to an article published in Nature, the ship alone would have changed Dimorphos's orbit by seven minutes, but the recoil and ejecta produced by the collision reduced it even more. According to a second analysis, the asteroid's surface material loss added between 2.2 and 4.9 times to the shift in momentum.

With enough time, warning, and resources, we can prevent an asteroid impact, according to Derek Richardson, an astronomy professor at the University of Maryland (UMD) and the working group leader for the DART investigation. "We can't stop hurricanes or earthquakes yet, but we ultimately learned that we can prevent an asteroid impact," he said. A comparatively minor shift in an asteroid's orbit could, given enough time, cause it to miss the Earth and avert widespread destruction of our world.

In order to allow space agencies enough time to prepare and carry out a kinetic impact mission, astronomers would need to detect the object in advance—"several years at a minimum, but ideally decades"—of their intended impact.

Potential threats aren't always simple to detect before they're nearby, despite numerous attempts being made to map near-Earth objects. For instance, a truck-sized asteroid that was only found a week before it passed a few thousand miles from Earth in January 2023 made one of the nearest passes ever documented.

It is more difficult to divert an object the closest it is to striking the Earth, Richardson told The Register. "Practically speaking, that implies that we would require a larger ship (or more than one), moving more quickly, and launched earlier than a threat further away. Therefore, the more alerts we receive, the better. We are unable to specify a precise upper limit because the size of the potentially dangerous item also plays a role. The larger the object, the stronger the strike we would need to use, etc."

However, the success of DART "builds confidence about humanity's ability to defend the Earth from an asteroid danger," experts wrote in a third article, which was also published in Nature. According to a fourth research, the expelled material left Dimorphos with a comet-like tail, converting it into a so-called "active" asteroid.

We still don't fully understand how Dimorphos and its progenitor asteroid Didymos were affected by the impact. DART had only a camera and was completely obliterated when it hit. In a follow-up journey in 2024, the European Space Agency will send its Hera probe to conduct a more thorough analysis of the binary asteroid system.

"The precise mass of Dimorphos is the [top] question the DART team wants answered, according to Richardson. "We will be able to determine the impact's effectiveness once we know that information combined with the trajectory shift that was witnessed. But there are many other things we would like to know, such as whether or not we created a crater that was so large that it greatly altered the moon's general shape. Did we substantially alter the moon's rotation?

"Is there any leftover material in the system's orbit? Did Didymos receive a significant quantity of material that had a discernible impact on its surface? What's Dimorphos' interior structure like—is it a pile of debris from top to bottom or just on the surface? What can we infer about the formation of asteroid moons and the long-term evolution of those moons?"

Experts are developing new technologies that could be used to divert an object in space as part of their efforts to improve planetary defense strategies. According to UMD Principal Research Scientist Tony Farnham, efforts are being made to identify possible targets for testing asteroid-bumping devices in the future.

He informed us "Apophis will be investigated during its passing in 2029, and preparations call for the OSIRIS-Rex spacecraft to be diverted in order to converge on the asteroid. O-Rex will describe its physical characteristics and investigate what transpires to the Apophis during the pass of the Earth."